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Cycles: Remove MultiGGX code, replace with albedo scaling #107958

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Lukas Stockner merged 8 commits from LukasStockner/blender:remove-multiggx into main 2023-06-05 02:21:03 +02:00
Conversation 7 Commits 8 Files Changed 24 +40 -13
1 changed files with 40 additions and 13 deletions
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Showing only changes of commit 807a0eb0d6 - Show all commits

53
intern/cycles/kernel/closure/bsdf_microfacet.h
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@ -52,8 +52,18 @@ typedef struct MicrofacetBsdf {
SHADER_CLOSURE_BASE;
float alpha_x, alpha_y, ior;
/* Used to account for missing energy due to the single-scattering microfacet model.
* This could be included in bsdf->weight as well, but there it would mess up the color
* channels.
* Note that this is currently only used by GGX. */
float energy_scale;
/* Fresnel model to apply, as well as the extra data for it.
* For NONE and DIELECTRIC, no extra storage is needed, so the pointer is NULL for them. */
int fresnel_type;
ccl_private void *fresnel;
float3 T;
} MicrofacetBsdf;
@ -296,28 +306,37 @@ ccl_device_inline void microfacet_ggx_preserve_energy(KernelGlobals kg,
E_avg = 1.0f;
}
/* Check if we need to account for extra saturation due to multi-bounce Fresnel. */
if (Fss == one_spectrum()) {
bsdf->weight *= 1.0f + ((1.0f - E) / E);
}
else {
const float missing_factor = ((1.0f - E) / E);
bsdf->energy_scale = 1.0f + missing_factor;
/* Check if we need to account for extra darkening/saturation due to multi-bounce Fresnel. */
if (Fss != one_spectrum()) {
/* Fms here is based on the appendix of "Revisiting Physically Based Shading at Imageworks"
* by Christopher Kulla and Alejandro Conty,
* with one Fss cancelled out since this is just a multiplier on top of
* the single-scattering BSDF, which already contains one bounce of Fresnel. */
const Spectrum Fms = Fss * E_avg / (one_spectrum() - Fss * (1.0f - E_avg));
bsdf->weight *= one_spectrum() + Fms * ((1.0f - E) / E);
/* Since we already include the energy compensation in bsdf->energy_scale,
* this term is what's needed to make the full BSDF * weight * energy_scale
* computation work out to the correct value. */
const Spectrum darkening = (one_spectrum() + Fms * missing_factor) / bsdf->energy_scale;
bsdf->weight *= darkening;
bsdf->sample_weight *= average(darkening);
}
/* TODO: Ensure that increase in weight does not mess up glossy color, albedo etc. passes */
}
/* This function estimates the albedo of the BSDF (NOT including the bsdf->weight) as caused by
* the applied Fresnel model for the given view direction.
* The base microfacet model is assumed to have an albedo of 1, but e.g. a reflection-only
* closure with Fresnel applied can end up having a very low overall albedo.
* The base microfacet model is assumed to have an albedo of 1 (we have the energy preservation
* code for that), but e.g. a reflection-only closure with Fresnel applied can end up having
* a very low overall albedo.
* This is used to adjust the sample weight, as well as for the Diff/Gloss/Trans Color pass
* and the Denoising Albedo pass. */
* and the Denoising Albedo pass.
*
* NOTE: This code assumes the microfacet surface is fairly smooth. For very high roughness,
* the results are much more uniform across the surface.
* For better results, we'd be blending between this and Fss based on roughness, but that
* would involve storing or recomputing Fss, which is probably not worth it. */
ccl_device Spectrum bsdf_microfacet_estimate_fresnel(ccl_private const ShaderData *sd,
ccl_private const MicrofacetBsdf *bsdf)
{
@ -818,6 +837,7 @@ ccl_device int bsdf_microfacet_ggx_setup(ccl_private MicrofacetBsdf *bsdf)
bsdf->alpha_y = saturatef(bsdf->alpha_y);
bsdf->fresnel_type = MicrofacetFresnel::NONE;
bsdf->energy_scale = 1.0f;
bsdf->type = CLOSURE_BSDF_MICROFACET_GGX_ID;
return SD_BSDF | SD_BSDF_HAS_EVAL;
@ -830,6 +850,7 @@ ccl_device int bsdf_microfacet_ggx_clearcoat_setup(ccl_private MicrofacetBsdf *b
bsdf->alpha_y = bsdf->alpha_x;
bsdf->fresnel_type = MicrofacetFresnel::DIELECTRIC;
bsdf->energy_scale = 1.0f;
bsdf->type = CLOSURE_BSDF_MICROFACET_GGX_CLEARCOAT_ID;
bsdf->sample_weight *= average(bsdf_microfacet_estimate_fresnel(sd, bsdf));
@ -842,6 +863,7 @@ ccl_device int bsdf_microfacet_ggx_refraction_setup(ccl_private MicrofacetBsdf *
bsdf->alpha_y = bsdf->alpha_x;
bsdf->fresnel_type = MicrofacetFresnel::NONE;
bsdf->energy_scale = 1.0f;
bsdf->type = CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID;
return SD_BSDF | SD_BSDF_HAS_EVAL | SD_BSDF_HAS_TRANSMISSION;
@ -853,6 +875,7 @@ ccl_device int bsdf_microfacet_ggx_glass_setup(ccl_private MicrofacetBsdf *bsdf)
bsdf->alpha_y = bsdf->alpha_x;
bsdf->fresnel_type = MicrofacetFresnel::DIELECTRIC;
bsdf->energy_scale = 1.0f;
bsdf->type = CLOSURE_BSDF_MICROFACET_GGX_GLASS_ID;
return SD_BSDF | SD_BSDF_HAS_EVAL | SD_BSDF_HAS_TRANSMISSION;
@ -872,7 +895,8 @@ ccl_device Spectrum bsdf_microfacet_ggx_eval(ccl_private const ShaderClosure *sc
const float3 wo,
ccl_private float *pdf)
{
return bsdf_microfacet_eval<MicrofacetType::GGX>(sc, Ng, wi, wo, pdf);
ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
return bsdf->energy_scale * bsdf_microfacet_eval<MicrofacetType::GGX>(sc, Ng, wi, wo, pdf);
}
ccl_device int bsdf_microfacet_ggx_sample(ccl_private const ShaderClosure *sc,
@ -886,8 +910,11 @@ ccl_device int bsdf_microfacet_ggx_sample(ccl_private const ShaderClosure *sc,
ccl_private float2 *sampled_roughness,
ccl_private float *eta)
{
return bsdf_microfacet_sample<MicrofacetType::GGX>(
int label = bsdf_microfacet_sample<MicrofacetType::GGX>(
sc, path_flag, Ng, wi, rand, eval, wo, pdf, sampled_roughness, eta);
*eval *= ((ccl_private const MicrofacetBsdf *)sc)->energy_scale;
return label;
}
/* Beckmann microfacet with Smith shadow-masking from: